Am 28. März 2024 14:09:52 UTC schrieb Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>:
On 27/03/2024 07:09, Gerd Hoffmann wrote:
On Tue, Mar 26, 2024 at 01:30:48PM +0000, Mark Cave-Ayland wrote:
Heh I've actually been using isapc over the past couple of weeks to fire up some old programs in a Windows 3 VM :)
I'm wondering why these use cases can't simply use the 'pc' machine type?
The early pci chipsets of the 90-ies have been designed in a backward-compatible manner, with devices such as the IDE controller being mapped to the standard ISA ioports. So even an historic OS which does not know what PCI is can run on that hardware, by simply talking to devices using the standard ISA io ports ...
Hmmm that's a fair point: I think the pc machine has a PCI-ISA bridge included, so ISA devices can be plugged in as needed. The reason I ended up on that configuration was because I ended up chasing down a regression, and wanted to quickly eliminate things such as ACPI.
In theory you could pass `-M acpi=off` to not instantiate the PIIX4 ACPI function, essentially turning the Frankenstein-PIIX4 SB into a PIIX3. However, this also removes SMI registers used by SeaBIOS to handle SMM setup which may create unwanted side effects. On a real PIIX3, these registers are located in the ISA function. I wonder if it made sense to implement that for greater compatibility. What do you think? Gerd, what do you think w.r.t. SeaBIOS? Best regards, Bernhard
ATB,
Mark.